Conventionally, various circularly polarized antennas are put in practical use. For example, Patent Document 1 discloses a slot bow-tie antenna which transmits and receives a circularly polarized wave.
An antenna of Patent Document 1 includes a loop conductor and a conductive housing. The loop conductor has a substantially annular shape with a part of the circle lacking (C-shape). The housing is disposed to surround the loop conductor. A wall of the housing on a radiation surface side of the loop conductor is formed with bow-tie slots. The bow-tie slots overlap with the loop conductor in a perpendicular direction to the radiation surface of the loop conductor.
Further the antenna of Patent Document 1 includes a slot conductor formed with bow-tie slots, and a loop conductor. The slot conductor is formed on a first dielectric substrate, and the loop conductor is formed on a second dielectric substrate. The first and second dielectric substrates overlap with each other. Here, the loop conductor is disposed between the first and second dielectric substrates. The slot conductor faces the loop conductor via the first dielectric substrate.